Clodagh Kilcoyne / REUTERS
A general view shows the Lifford Bridge, where a customs unit was sited before the Good Friday Agreement, on the exact border between Strabane in Northern Ireland and Lifford in Ireland, August 2017.

A new fight has been brewing over the consequences of Brexit for the border between Northern Ireland and the neighboring Republic of Ireland. Both British and EU negotiators have identified the border as one of the key political questions that have to be addressed early on in negotiations. It’s easy not to have a border between two states that are both part of the EU’s single market (the regulatory regime that allows easy trade across the EU) and customs union (the arrangement under which European states do not impose customs duties on each other and maintain a common customs policy toward all other countries).

Now, however, the United Kingdom is leaving the European Union, which means that Ireland’s northern border is about to become the land boundary dividing Europe and Britain. That has dangerous consequences. Since the signing of the Good Friday peace deal in 1998, Northern Ireland’s economy has become increasingly intertwined with its southern neighbor, especially in key sectors such as agriculture. Even more important, Northern Ireland’s peace arrangements rely on Irish nationalists acquiescing to British rule, which might evaporate if barbed wire, police, and customs posts suddenly appear along the border.

In an effort to avoid such tensions, all the key players agree that there should be no hard border between the north and south. Yet their agreement hides sharp political divisions, which could lead to failed negotiations.

A FLEXIBLE CUSTOMS ARRANGEMENT?

Tensions among the negotiating parties have come to the surface thanks to two position papers on the border that the United Kingdom released last month. In the first paper, London makes clear that it wants the Irish border to be invisible. In the second, it lays out a broad but ill-defined vision for how new British-EU customs arrangements as a whole might work. The two papers, however, present an interlinked argument in which a broader customs “partnership” would be an essential precondition for any “invisible” and “open” border between Northern Ireland and